Abstract - The increasing numbers of endangered wild bee
species highlights the need for quantifying potential adverse effects of
foraging honeybees. We analysed the response of bumblebees at genus and
species level to experimentally increased honeybee density. The study was
carried out on a Phacelia tanacetifolia field and adjacent patches of wild plants located in an
agricultural landscape. Addition of one or ten A. m. ligustica colonies substantially
increased total honeybee density not only on Phacelia but also on neighbouring
patches of wild plants. The response of bumblebees (Bombus spp.) differed among
species. Only minor spatial changes in the abundance of the short-tongued
B. terrestris-group were observed on Phacelia. At wild plant patches, the B. lapidarius-group and the longer
tongued bumblebee species (B. muscorum, B. sylvarum, B. pascuorum) responded with a shift between plant
species. Limitations of competition avoidance in flower-impoverished
landscapes are discussed.